Thermally stable polycrystalline compacts for reduced spalling, earth-boring tools including such compacts, and related methods

FIELD

Embodiments of the present disclosure relate generally to polycrystalline compacts, such as polycrystalline diamond compacts, that have a volume that includes interstitial metal solvent catalyst material and another volume that does not include such interstitial metal solvent catalyst material, as well as to earth-boring tools including such compacts, and to related methods.

BACKGROUND

Cutting elements used in earth-boring tools often include polycrystalline diamond compact (often referred to as “PDC”) cutting elements, which are cutting elements that include a volume of polycrystalline diamond material. One or more surfaces of the volume of polycrystalline diamond material define one or more cutting surfaces of the PDC cutting element. Polycrystalline diamond material is material that includes inter-bonded grains or crystals of diamond material. In other words, polycrystalline diamond material includes direct, inter-granular diamond-to-diamond atomic bonds between the grains or crystals of diamond material. The terms “grain” and “crystal” are used synonymously and interchangeably herein.

PDC cutting elements are formed by sintering and bonding together relatively small diamond grains under conditions of high temperature and high pressure in the presence of a metal solvent catalyst (for example, cobalt, iron, nickel, or alloys or mixtures thereof) to form a layer or “table” of polycrystalline diamond material on a cutting element substrate. These processes are often referred to as high-temperature/high-pressure (or “HTHP”) processes. The cutting element substrate may comprise a cermet material (i.e., a ceramic-metal composite material) such as cobalt-cemented tungsten carbide. In such instances, the cobalt (or other catalyst material) in the cutting element substrate may diffuse into the spaces between the diamond grains during sintering and serve as the catalyst material for forming the inter-granular diamond-to-diamond bonds, and the resulting diamond table, from the diamond grains. In other methods, powdered catalyst material may be mixed with the diamond grains prior to sintering the grains together in an HTHP process.

Upon formation of a diamond table using an HTHP process, catalyst material may remain in interstitial spaces between the grains of diamond in the resulting polycrystalline diamond table. The presence of the catalyst material in the diamond table may contribute to thermal damage in the diamond table when the cutting element is heated during use due to friction at the contact point between the cutting element and the rock formation being cut.

PDC cutting elements in which the catalyst material remains in the diamond table are generally thermally stable up to a temperature of about 750° C., although internal stress within the cutting element may begin to develop at temperatures exceeding about 400° C. due to a phase change that occurs in cobalt at that temperature (a change from the “beta” phase to the “alpha” phase). Also beginning at about 400° C., there is an internal stress component that arises due to differences in the thermal expansion of the diamond grains and the catalyst material at the grain boundaries. This difference in thermal expansion may result in relatively large tensile stresses at the interface between the diamond grains, and may contribute to thermal degradation of the microstructure when PDC cutting elements are used in service. Differences in the thermal expansion between the diamond table and the cutting element substrate to which it is bonded may further exacerbate the stresses in the polycrystalline diamond compact. This differential in thermal expansion may result in relatively large compressive and/or tensile stresses at the interface between the diamond table and the substrate that eventually leads to the deterioration of the diamond table, causes the diamond table to delaminate from the substrate, or results in the general ineffectiveness of the cutting element.

Furthermore, at temperatures at or above about 750° C., some of the diamond crystals within the diamond table may react with the catalyst material causing the diamond crystals to undergo a chemical breakdown or conversion to another allotrope of carbon. For example, the diamond crystals may graphitize at the diamond crystal boundaries, which may substantially weaken the diamond table. Also, at extremely high temperatures, in addition to graphite, some of the diamond crystals may be converted to carbon monoxide and/or carbon dioxide.

In order to reduce the problems associated with differences in thermal expansion and chemical breakdown of the diamond crystals in PDC cutting elements, so-called “thermally stable” polycrystalline diamond compacts (which are also known as thermally stable products, or “TSPs”) have been developed. Such a TSP may be formed by leaching or otherwise removing the catalyst material (e.g., cobalt) out from interstitial spaces between the inter-bonded diamond crystals in the diamond table using, for example, an acid or combination of acids (e.g., aqua regia). A substantial amount of the catalyst material may be removed from the diamond table, or catalyst material may be removed from only a portion thereof. TSPs in which substantially all catalyst material has been leached out from the diamond table have been reported to be thermally stable up to temperatures of about 1,200° C. It has also been reported, however, that such fully leached diamond tables are relatively more brittle and vulnerable to shear, compressive, and tensile stresses than are non-leached diamond tables. In addition, it may be difficult to secure a completely leached diamond table to a supporting substrate. In an effort to provide cutting elements having diamond tables that are more thermally stable relative to non-leached diamond tables, but that are also relatively less brittle and vulnerable to shear, compressive, and tensile stresses relative to fully leached diamond tables, cutting elements have been provided that include a diamond table in which the catalyst material has been leached from a portion or portions of the diamond table. For example, it is known to leach catalyst material from the cutting face, from the side of the diamond table, or both, to a desired depth within the diamond table, but without leaching all of the catalyst material out from the diamond table.

BRIEF SUMMARY

In some embodiments, the present disclosure includes a generally planar polycrystalline compact comprising a body of inter-bonded grains of hard material. The body of inter-bonded grains of hard material has a first major surface defining a front cutting face of the polycrystalline compact, a second major surface on an opposing back side of the body, at least one lateral side surface extending between the first major surface and the second major surface, and a central axis extending through a center of the body and generally perpendicular to the first major surface and the second major surface. The hard material of the inter-bonded grains of hard material comprises diamond or cubic boron nitride. The polycrystalline compact further includes an interstitial material. A first volume of the polycrystalline compact is at least substantially free of the interstitial material, such that voids exist in interstitial spaces between surfaces of the inter-bonded grains of hard material within the first volume. A second volume of the polycrystalline compact includes the interstitial material in interstitial spaces between surfaces of the inter-bonded grains of hard material within the second volume. An interface between the first volume and the second volume is configured, located and oriented such that at least one crack originating proximate a point of contact between the polycrystalline compact and a subterranean formation near the at least one lateral side surface of the body and propagating along the interface generally toward the central axis will propagate generally toward the second major surface of the body at an acute angle or angles to each of the first major surface and the second major surface.

In another embodiment, an earth-boring tool comprises a tool body and a plurality of cutting elements attached to the tool body, wherein at least one cutting element of the plurality of cutting elements comprises a polycrystalline compact as described in the above paragraph.

In additional embodiments, the present disclosure includes a method of forming a polycrystalline compact comprising a body of inter-bonded grains of hard material. In accordance with the method, a high-temperature/high-pressure (HTHP) sintering process is used to form a body of inter-bonded grains of hard material having a first major surface defining a front cutting face of the polycrystalline compact, a second major surface on an opposing back side of the body, at least one lateral side surface extending between the first major surface and the second major surface, and a central axis extending through a center of the body and generally perpendicular to the first major surface and the second major surface. The hard material is selected to comprise diamond or cubic boron nitride. During the HTHP sintering process, the formation of inter-granular bonds between the inter-bonded grains of hard material is catalyzed using a catalyst, and the catalyst forms an interstitial material in the resulting body of inter-bonded grains of hard material. The interstitial material is removed from interstitial spaces between surfaces of the inter-bonded grains of hard material within the first volume, and the interstitial material is left in interstitial spaces between surfaces of the inter-bonded grains of hard material within the second volume, such that the first volume is at least substantially free of the interstitial material and voids exist in the interstitial spaces between surfaces of the inter-bonded grains of hard material within the first volume. An interface is formed between the first volume and the second volume that is configured, located and oriented such that at least one crack originating proximate a point of contact between the polycrystalline compact and a subterranean formation near the at least one lateral side surface of the body, and propagating along the interface generally toward the central axis, will propagate generally toward the second major surface at an acute angle or angles to each of the first major surface and the second major surface.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing out and distinctly claiming what are regarded as embodiments of the invention, various features and advantages of embodiments of the disclosure may be more readily ascertained from the following description of some embodiments of the disclosure when read in conjunction with the accompanying drawings, in which:

<figref idref="DRAWINGS">FIG. 1</figref> is a simplified partially cut-away perspective view of an embodiment of a PDC cutting element including a generally planar polycrystalline compact of the disclosure;

<figref idref="DRAWINGS">FIG. 2</figref> is a cross-sectional side view of the PDC cutting element of <figref idref="DRAWINGS">FIG. 1</figref>;

<figref idref="DRAWINGS">FIG. 3</figref> is a simplified drawing illustrating how a microstructure of a first volume of the polycrystalline compact of the PDC cutting element of <figref idref="DRAWINGS">FIGS. 1 and 2</figref> may appear under magnification and illustrates voids in interstitial spaces between inter-bonded grains of hard material;

<figref idref="DRAWINGS">FIG. 4</figref> is a simplified drawing illustrating how a microstructure of a second volume of the polycrystalline compact of the PDC cutting element of <figref idref="DRAWINGS">FIGS. 1 and 2</figref> may appear under magnification and illustrates interstitial material in the interstitial spaces between inter-bonded grains of hard material;

<figref idref="DRAWINGS">FIG. 5</figref> is an enlarged view of a portion of the PDC cutting element of <figref idref="DRAWINGS">FIGS. 1 and 2</figref> including the polycrystalline compact thereof;

<figref idref="DRAWINGS">FIGS. 6A through 6F</figref> are simplified cross-sectional side views illustrating an example embodiment of a method that may be used form a polycrystalline compact of a PDC cutting element as described herein;

<figref idref="DRAWINGS">FIGS. 7A through 7F</figref> are simplified cross-sectional side views illustrating another example embodiment of a method that may be used form a polycrystalline compact of a PDC cutting element as described herein;

<figref idref="DRAWINGS">FIG. 8</figref> is a simplified cross-sectional side view of another embodiment of a PDC cutting element including a generally planar polycrystalline compact of the disclosure;

<figref idref="DRAWINGS">FIG. 9</figref> is a simplified cross-sectional side view of another embodiment of a PDC cutting element including a generally planar polycrystalline compact of the disclosure and having a mask layer over the polycrystalline compact in preparation for a leaching process; and

<figref idref="DRAWINGS">FIG. 10</figref> is a simplified perspective view of an earth-boring tool in the form of a rotary drill bit that may include a plurality of PDC cutting elements as described herein.

DETAILED DESCRIPTION

The illustrations presented herein are not actual views of any particular cutting element or earth-boring tool, and are not drawn to scale, but are merely idealized representations that are employed to describe embodiments of the disclosure. Elements common between figures may retain the same numerical designation.

As used herein, relational terms, such as “first,” “second,” “top,” “bottom,” “upper,” “lower,” “over,” “under,” etc., are used for clarity and convenience in understanding the disclosure and accompanying drawings and does not connote or depend on any specific preference, orientation, or order, except where the context clearly indicates otherwise.

As used herein, the term “substantially,” in reference to a given parameter, property, or condition, means to a degree that one skilled in the art would understand that the given parameter, property, or condition is met with a small degree of variance, such as within acceptable manufacturing tolerances.

As used herein, the term “configured” refers to a shape, material composition, and arrangement of one or more of at least one structure and at least one apparatus facilitating operation, response to an external stimulus, or both, of one or more of the structure and the apparatus in a pre-determined or intended way.

As used herein, the terms “earth-boring tool” means and includes any type of bit or tool used for drilling during the formation or enlargement of a wellbore in a subterranean formation and includes, for example, fixed-cutter bits, roller cone bits, percussion bits, core bits, eccentric bits, bicenter bits, reamers, mills, drag bits, hybrid bits (e.g., rolling components in combination with fixed cutting elements), and other drilling bits and tools known in the art.

As used herein, the term “polycrystalline material” means and includes any material comprising a plurality of grains (i.e., crystals) of the material that are bonded directly together by inter-granular bonds. The crystal structures of the individual grains of the material may be randomly oriented in space within the polycrystalline material.

As used herein, the term “polycrystalline compact” means and includes any structure comprising a polycrystalline material formed by a process that involves application of pressure (e.g., compaction) to the precursor material or materials used to form the polycrystalline material.

As used herein, the term “inter-granular bond” means and includes any direct atomic bond (e.g., covalent, ionic, metallic, etc.) between atoms in adjacent grains of hard material.

As used herein, the ten “hard material” means and includes any material having a Knoop hardness value of greater than or equal to about 3,000 Kg_f/mm²(29,420 MPa). Non-limiting examples of hard materials include diamond (e.g., natural diamond, synthetic diamond, or combinations thereof) and cubic boron nitride.

As used herein, the term “grain size” means and includes a geometric mean diameter measured from a 2D section through a bulk material. The geometric mean diameter for a group of particles may be determined using techniques known in the art, such as those set forth in Ervin E. Underwood, <i>Quantitative Stereology, </i>103-105 (Addison-Wesley Publishing Company, Inc. 1970), which is incorporated herein in its entirety by this reference.

<figref idref="DRAWINGS">FIG. 1</figref> is a partially cut-away perspective view of a PDC cutting element <b>100</b> that includes a generally planar polycrystalline compact <b>102</b> bonded to a supporting substrate <b>104</b> at an interface <b>106</b>. In additional embodiments, the polycrystalline compact <b>102</b> may be formed and/or employed without the supporting substrate <b>104</b>. As depicted in <figref idref="DRAWINGS">FIG. 1</figref>, the cutting element <b>100</b> may be cylindrical or disc-shaped. In additional embodiments, the cutting element <b>100</b> may have a different shape, such as a dome, cone, or chisel shape.

The supporting substrate <b>104</b> may have a first end surface <b>114</b>, a second end surface <b>116</b>, and a generally cylindrical lateral side surface <b>118</b> extending between the first end surface <b>114</b> and the second end surface <b>116</b>. As depicted in <figref idref="DRAWINGS">FIG. 1</figref>, the first end surface <b>114</b> and the second end surface <b>116</b> may be substantially planar. In additional embodiments, the first end surface <b>114</b> and/or the second end surface <b>116</b> (and, hence, the interface <b>106</b> between the supporting substrate <b>104</b> and the polycrystalline compact <b>102</b>) may be non-planar. In addition, as shown in <figref idref="DRAWINGS">FIG. 1</figref>, the supporting substrate <b>104</b> may have a generally cylindrical shape. In additional embodiments, the supporting substrate <b>104</b> may have a different shape, such as a dome, cone, or chisel shape.

The supporting substrate <b>104</b> may be formed of and include a material that is relatively hard and resistant to wear. By way of non-limiting example, the supporting substrate <b>104</b> may be formed from and include a ceramic-metal composite material (which are often referred to as “cermet” materials). In some embodiments, the supporting substrate <b>104</b> is formed of and includes a cemented carbide material, such as a cemented tungsten carbide material, in which tungsten carbide particles are cemented together in a metallic binder material. As used herein, the teem “tungsten carbide” means any material composition that contains chemical compounds of tungsten and carbon, such as, for example, WC, W₂C, and combinations of WC and W₂C. Tungsten carbide includes, for example, cast tungsten carbide, sintered tungsten carbide, and macrocrystalline tungsten carbide. The metallic binder material may include, for example, a catalyst material such as cobalt, nickel, iron, or alloys and mixtures thereof. In at least some embodiments, the supporting substrate <b>104</b> is formed of and includes a cobalt-cemented tungsten carbide material.

The polycrystalline compact <b>102</b> may be disposed on or over the second end surface <b>116</b> of the supporting substrate <b>104</b>. The polycrystalline compact <b>102</b> includes a body of inter-bonded grains of hard material, and has a first major surface <b>108</b> defining the front cutting face of the polycrystalline compact <b>102</b>, a second major surface <b>109</b> on an opposing back side of the body, and at least one lateral side surface <b>110</b> extending between the first major surface <b>108</b> and the second major surface <b>109</b>. As shown in <figref idref="DRAWINGS">FIG. 2</figref>, a central axis A may be defined that extends through a center of the body of the polycrystalline compact <b>102</b> and generally perpendicular to the first major surface <b>108</b> and the second major surface <b>109</b>.

The polycrystalline compact <b>102</b> may also include a chamfered edge <b>112</b> at a periphery of the cutting face <b>108</b>. The chamfered edge <b>112</b> shown in <figref idref="DRAWINGS">FIG. 1</figref> has a single chamfer surface, although the chamfered edge <b>112</b> also may have additional chamfer surfaces, and such chamfer surfaces may be oriented at chamfer angles that differ from the chamfer angle of the chamfered edge <b>112</b>, as known in the art. Further, in lieu of a chamfered edge <b>112</b>, one or more edges of the polycrystalline compact <b>102</b> may be rounded or comprise a combination of at least one chamfer surface and at least one arcuate surface.

As illustrated in <figref idref="DRAWINGS">FIG. 1</figref>, the lateral side surface <b>110</b> of the polycrystalline compact <b>102</b> may be substantially coplanar with the lateral side surface <b>118</b> of the supporting substrate <b>104</b>, and the cutting face <b>108</b> of the polycrystalline compact <b>102</b> may extend parallel to the first end surface <b>114</b> of the supporting substrate <b>104</b>. Accordingly, the polycrystalline compact <b>102</b> may be cylindrical or disc-shaped. In additional embodiments, the polycrystalline compact <b>102</b> may have a different shape, such as a dome, cone, or chisel shape. The polycrystalline compact <b>102</b> may have a thickness within range of from about 1 millimeter (mm) to about 4 mm, such as from about 1.5 mm to about 3.0 mm. In some embodiments, the polycrystalline compact <b>102</b> has a thickness in the range of about 1.8 mm to about 2.2 mm.

The inter-bonded grains of hard material (i.e., the polycrystalline material of the polycrystalline compact <b>102</b>) may comprise, for example, diamond or cubic boron nitride. The polycrystalline material may comprise more than about seventy percent (70%) by volume of the polycrystalline compact <b>102</b>, more than about eighty percent (80%) by volume of the polycrystalline compact <b>102</b>, or even more than about ninety percent (90%) by volume of the polycrystalline compact <b>102</b>. The grains or crystals of the hard polycrystalline material are bonded together to form the polycrystalline compact <b>102</b>.

Interstitial spaces or regions between the grains of hard material may be filled with an interstitial material (e.g., a metal solvent catalyst) in one or more regions of the polycrystalline compact <b>102</b>, while voids may be present in the interstitial spaces or regions between the grains of hard material in one or more other regions of the polycrystalline compact <b>102</b>.

The polycrystalline compact <b>102</b> may be formed using an HTHP sintering process to bond together relatively small diamond (synthetic, natural or a combination) or cubic boron nitride grains, termed “grit,” under conditions of high temperature and high pressure in the presence of a catalyst (e.g., cobalt, iron, nickel, or alloys and mixtures thereof). The metal solvent catalyst material used to catalyze the formation of the inter-granular bonds between the grains of hard material may remain in interstitial spaces between the inter-bonded grains of hard material. The metal solvent catalyst material may be leached out of the interstitial spaces using, for example, an acid or combination of acids (e.g., aqua regia) to form and define first and second regions within the polycrystalline compact <b>102</b>, including a first leached region and a second unleached region, as discussed in further detail below.

For example, with reference to <figref idref="DRAWINGS">FIGS. 1 and 2</figref>, the polycrystalline compact <b>102</b> may include a leached first volume <b>120</b> and an unleached second volume <b>122</b>. The first volume <b>120</b> may comprise an outer region of the polycrystalline compact <b>102</b>, and may define the entire front cutting face <b>108</b> and at least a portion (all or only a portion) of the lateral side surface <b>110</b> of the polycrystalline compact <b>102</b>. The second volume <b>122</b> may comprise an inner region of the polycrystalline compact <b>102</b>, and may define at least a substantial majority of the second major surface <b>109</b> of the polycrystalline compact <b>102</b>.

<figref idref="DRAWINGS">FIG. 3</figref> is a simplified figure illustrating how a microstructure of the hard polycrystalline material in the first volume <b>120</b> of the polycrystalline compact <b>102</b> may appear under magnification, and <figref idref="DRAWINGS">FIG. 4</figref> is a similar figure illustrating how a microstructure of the hard polycrystalline material in the second volume <b>122</b> of the polycrystalline compact <b>102</b> may appear under magnification.

As shown in <figref idref="DRAWINGS">FIG. 3</figref>, the hard polycrystalline material in the first volume <b>120</b> may be at least substantially free of any interstitial material between inter-bonded grains of hard material <b>124</b>, such that voids <b>126</b> are defined in the interstitial spaces between surfaces of the inter-bonded grains of hard material <b>124</b> within the first volume <b>120</b>. As shown in <figref idref="DRAWINGS">FIG. 4</figref>, the hard polycrystalline material in the second volume <b>122</b> of the polycrystalline compact <b>102</b> includes interstitial material <b>128</b> in the interstitial spaces between surfaces of the inter-bonded grains of hard material <b>124</b> within the second volume <b>122</b>.

The interstitial material <b>128</b> may comprise a metal-solvent catalyst, such as iron, cobalt, nickel, or an alloy or mixture based on one or more such elements. In other embodiments, the interstitial material <b>128</b> may comprise another metal, a ceramic material, or any other material.

Referring again to <figref idref="DRAWINGS">FIG. 2</figref>, in accordance with embodiments of the present disclosure, an interface <b>130</b> between the first volume <b>120</b> and the second volume <b>122</b> of the polycrystalline compact <b>102</b> is configured, located and oriented such that one or more cracks originating proximate a point of contact between the polycrystalline compact <b>102</b> and a formation near the at least one lateral side surface <b>110</b> (e.g., near the chamfered edge <b>112</b>) of the body of inter-bonded grains of hard material <b>124</b> (<figref idref="DRAWINGS">FIGS. 3 and 4</figref>) and propagating along the interface <b>130</b> generally toward the central axis A will propagate generally toward the second major surface <b>109</b> of the body at an acute angle or angles to each of the first major surface <b>108</b> and the second major surface <b>109</b> of the polycrystalline compact <b>102</b>.

<figref idref="DRAWINGS">FIG. 5</figref> is an enlarged view of the polycrystalline compact <b>102</b> of the PDC cutting element <b>100</b> of <figref idref="DRAWINGS">FIGS. 1 and 2</figref>. As shown in <figref idref="DRAWINGS">FIG. 5</figref>, during use of the cutting element <b>100</b> in cutting a subterranean formation, cracks may originate within the polycrystalline compact <b>102</b> proximate the at least one lateral side surface <b>110</b> and the chamfered edge <b>112</b>. Applicant has observed that such cracks may have a tendency to propagate along the interface <b>130</b> between the first region <b>120</b> and the second region <b>122</b> of the polycrystalline compact <b>102</b>. Such cracks can lead to spalling of the polycrystalline material, which can reduce the efficacy of the cutting elements and, in some instances, render them unsuitable for use.

As shown in <figref idref="DRAWINGS">FIG. 5</figref>, according to embodiments of the disclosure, the interface <b>130</b> between the first volume <b>120</b> and the second volume <b>122</b> of the polycrystalline compact <b>102</b> is located and oriented such that the cracks propagate along the interface <b>130</b> in a direction represented by the arrow <b>132</b> generally toward the central axis A, and generally toward the second major surface <b>109</b>, and at an acute angle α to the second major surface <b>109</b> of the polycrystalline compact <b>102</b> and an acute angle β to the first major surface <b>108</b> of the polycrystalline compact <b>102</b>. The acute angle α and the acute angle β may be equal or non-equal to one another, depending on the particular configuration of the polycrystalline compact <b>102</b>.

Stated another way, in some embodiments, the interface <b>130</b> between the first volume <b>120</b> and the second volume <b>122</b> may have a dish shape. Further, the interface <b>130</b> between the first volume <b>120</b> and the second volume <b>122</b> may have a smooth profile or a stepped profile in a plane containing the central axis A, such as the plane of the cross-sectional view of <figref idref="DRAWINGS">FIG. 2</figref>.

In this configuration, an annular portion of the interface <b>130</b> between the first volume <b>120</b> and the second volume <b>122</b> is located a distance <b>134</b> from the second major surface <b>109</b> of the body of inter-bonded grains of hard material, and regions of the interface <b>130</b> circumscribed by the annular portion are located at one or more distances <b>136</b> from the second major surface <b>109</b> of the body of inter-bonded grains of hard material. Each of the one or more distances <b>136</b> may be shorter than the first distance <b>134</b>, as shown in <figref idref="DRAWINGS">FIG. 5</figref>.

In such embodiments, a first portion of the interface <b>130</b> between the first volume <b>120</b> and the second volume <b>122</b> is located at a first distance <b>134</b> from the second major surface <b>109</b> of the body of inter-bonded grains of hard material and at a second distance <b>140</b> from the central axis A of the body of inter-bonded grains of hard material, and a second portion of the interface <b>130</b> between the first volume <b>120</b> and the second volume <b>122</b> is located at a third distance <b>136</b> from the second major surface <b>109</b> of the body of inter-bonded grains of hard material and at a fourth distance <b>142</b> from the central axis A of the body of inter-bonded grains of hard material. As shown in <figref idref="DRAWINGS">FIG. 5</figref>, the first distance <b>134</b> is greater than the third distance <b>136</b>, and the second distance <b>140</b> may be greater than the fourth distance <b>142</b>.

As shown in <figref idref="DRAWINGS">FIG. 5</figref>, the first major surface <b>108</b> of the polycrystalline compact <b>102</b>, which comprises a body of inter-bonded grains of hard material <b>124</b> (<figref idref="DRAWINGS">FIGS. 3 and 4</figref>), may comprise a surface of the first volume <b>120</b> of the polycrystalline compact <b>102</b>, and the second major surface <b>109</b> of the polycrystalline compact <b>102</b> may comprise a surface of the second volume <b>122</b> of the polycrystalline compact <b>102</b>. At least a portion of the at least one lateral side surface <b>110</b> of the polycrystalline compact <b>102</b> may comprise another surface of the first volume <b>120</b> of the polycrystalline compact <b>102</b>. In some embodiments, only a portion of the lateral side surface <b>110</b> of the polycrystalline compact <b>102</b> extending from the chamfered edge <b>112</b> toward the interface <b>106</b> comprises a surface of the first volume <b>120</b> of the polycrystalline compact <b>102</b>, and another portion of the lateral side surface <b>110</b> of the polycrystalline compact <b>102</b> adjacent the interface <b>106</b> comprises a surface of the second volume <b>122</b> of the polycrystalline compact <b>102</b>. In other embodiments, the entire lateral side surface <b>110</b> of the polycrystalline compact <b>102</b> may comprise a surface of the first volume <b>120</b> of the polycrystalline compact <b>102</b>, or may comprise a surface of the second volume <b>122</b> of the polycrystalline compact <b>102</b>.

Additional embodiments of the present disclosure include methods of making polycrystalline compacts for cutting elements as described herein. In some embodiments, controlled leaching of interstitial material <b>128</b> (<figref idref="DRAWINGS">FIG. 4</figref>) of from interstitial spaces between the inter-bonded grains of hard material <b>124</b> may be used to form the first volume <b>120</b> to have a configuration as described herein. <figref idref="DRAWINGS">FIGS. 6A through 6F</figref> illustrate a first example of an embodiment of such a method, and <figref idref="DRAWINGS">FIGS. 7A through 7F</figref> illustrate another example of an embodiment of such a method.

<figref idref="DRAWINGS">FIG. 6A</figref> is a simplified cross-sectional side view similar to that of <figref idref="DRAWINGS">FIG. 5</figref> and illustrates a portion of a PDC cutting element <b>200</b> that includes a polycrystalline compact <b>202</b> on a substrate <b>204</b>. The polycrystalline compact <b>202</b> and the substrate <b>204</b> may be as previously described in relation to the polycrystalline compact <b>102</b> and the substrate <b>104</b> with reference to <figref idref="DRAWINGS">FIGS. 1 through 5</figref>, with the exception that the polycrystalline compact <b>202</b> may be initially unleached, such that the entirety of the polycrystalline compact <b>202</b> includes interstitial material <b>128</b> (e.g., a metal solvent catalyst material) in the interstitial spaces between the inter-bonded grains of hard material <b>124</b> of the polycrystalline compact <b>202</b>. Thus, the entire volume of the polycrystalline compact <b>202</b> may initially be like the second volume <b>122</b> of the polycrystalline compact <b>102</b> of <figref idref="DRAWINGS">FIGS. 1 through 5</figref>. Only a portion of the substrate <b>204</b> is shown in <figref idref="DRAWINGS">FIG. 6A</figref> (and <figref idref="DRAWINGS">FIGS. 6B through 6F</figref>), similar to the view of <figref idref="DRAWINGS">FIG. 5</figref>.

As shown in <figref idref="DRAWINGS">FIG. 6A</figref>, a patterned mask <b>260</b>A may be formed over the polycrystalline compact <b>202</b>. The patterned mask <b>260</b>A may comprise a layer of material that is impermeable to a leaching agent used to leach interstitial material <b>128</b> out from the interstitial spaces between the grains of hard material <b>124</b> within what will become a leached first region <b>220</b> of the polycrystalline compact <b>202</b>. As a non-limiting example, the patterned mask <b>260</b>A may comprise a polymer material, such as an epoxy. At least one aperture <b>262</b>A may be formed or otherwise provided through the patterned mask <b>260</b>A, such that an area of the first major surface <b>208</b> of the polycrystalline compact <b>202</b> is exposed through the aperture <b>262</b>A. The polycrystalline compact <b>202</b> then may be immersed in or otherwise exposed to an leaching agent (e.g., an acid), such that the leaching agent may be allowed to leach and remove the interstitial material <b>128</b> (e.g., metal solvent catalyst) out from the interstitial spaces between the grains of hard material <b>124</b> within the polycrystalline compact <b>202</b> and form a first region <b>220</b> within the polycrystalline compact <b>202</b>. Such leaching agents are known in the art. As shown in <figref idref="DRAWINGS">FIG. 6A</figref>, the aperture <b>262</b>A may comprise a single hole through the patterned mask <b>260</b>A that is centered about (or proximate) the central axis A of the PDC cutting element <b>200</b>. A second volume <b>222</b> of the polycrystalline compact <b>202</b> comprises the unleached portion of the polycrystalline compact <b>202</b>. The polycrystalline compact <b>202</b> may be subjected to the leaching agent for a time sufficient to leach into the polycrystalline compact <b>202</b> to a selected depth, as measured as a distance from the first major surface <b>208</b> of the polycrystalline compact <b>202</b>. After the leaching process, the patterned mask <b>260</b>A may be removed.

As shown in <figref idref="DRAWINGS">FIG. 6B</figref>, a second patterned mask <b>260</b>B may be formed over the polycrystalline compact <b>202</b>, which may be similar to the first patterned mask <b>260</b>A, but the second patterned mask <b>260</b>B may have an annular aperture <b>262</b>B formed or otherwise provided through the patterned mask <b>260</b>B adjacent, but located radially, circumferentially around and above the first volume <b>220</b> as formed in the first leaching process carried out as described with reference to <figref idref="DRAWINGS">FIG. 6A</figref>. The polycrystalline compact <b>202</b> then may be again leached through the aperture <b>262</b>B so as to extend the leached portion of the polycrystalline compact <b>202</b> in the radial direction and enlarge the first volume <b>220</b> of the polycrystalline compact <b>202</b>, as shown in <figref idref="DRAWINGS">FIG. 6B</figref>. The duration of the leaching process of <figref idref="DRAWINGS">FIG. 6B</figref> may be shorter than the duration of the leaching process of <figref idref="DRAWINGS">FIG. 6A</figref>, such that the depth of the leached portion (i.e., the first volume <b>220</b>) is shallower in the regions formed by the leaching process of <figref idref="DRAWINGS">FIG. 6B</figref> compared to the regions formed by the leaching process of <figref idref="DRAWINGS">FIG. 6A</figref>.

This masking and leaching process may be repeated as shown in <figref idref="DRAWINGS">FIGS. 6C through 6E</figref> using patterned masks <b>260</b>C-<b>260</b>E respectively, each having an annular aperture <b>262</b>C-<b>262</b>E of increasing radius (and distance from the central axis A). Additionally, the durations of the leaching processes may be progressively shorter to cause the leach depth, and hence, the depth of the first volume <b>220</b> to become progressively shallower moving in the radial directions extending from the central axis A toward a lateral side surface <b>210</b> of the polycrystalline compact <b>202</b>. After completing the leaching processes, the last patterned mask layer may be removed to form the PDC cutting element <b>200</b> and the polycrystalline compact <b>202</b> of <figref idref="DRAWINGS">FIG. 6F</figref>, which is substantially similar to the PDC cutting element <b>100</b> and the polycrystalline compact <b>102</b> of <figref idref="DRAWINGS">FIGS. 1 through 5</figref>, but wherein an interface <b>230</b> between the first volume <b>220</b> and the second volume <b>222</b> has a stepped profile in a plane containing the central axis A, such as the plane of the cross-sectional view of <figref idref="DRAWINGS">FIG. 6F</figref>.

In the method described with reference to <figref idref="DRAWINGS">FIGS. 6A through 6F</figref>, the regions of the polycrystalline compact <b>202</b> that have been leached (e.g., the first volume <b>220</b>) are substantially shielded from the leaching agent by the patterned mask layer in subsequent leaching processes, and the shape of the interface <b>230</b> is achieved by varying the durations of the different leaching processes. In additional embodiments, the shape of the interface <b>230</b> may be attained using other methods, such as by varying the strength of the leaching agent.

<figref idref="DRAWINGS">FIGS. 7A through 7F</figref> illustrate another method that may be used to form a PDC cutting element <b>300</b> that includes a polycrystalline compact <b>302</b> similar to those previously described herein. The method of <figref idref="DRAWINGS">FIGS. 7A through 7F</figref> is similar to the method of <figref idref="DRAWINGS">FIGS. 6A through 6F</figref>, and involves the use of sequential masking and leaching processes using patterned masks <b>360</b>A-<b>360</b>E having apertures <b>362</b>A-<b>362</b>E therethrough, as shown in <figref idref="DRAWINGS">FIGS. 7A through 7E</figref>, respectively. In the method of <figref idref="DRAWINGS">FIGS. 7A through 7F</figref>, however, each of the apertures <b>362</b>A-<b>362</b>E comprises a single hole extending through each respective mask layer <b>360</b>A-<b>360</b>E, and each of the holes has a sequentially larger diameter moving from the first patterned mask layer <b>360</b>A of <figref idref="DRAWINGS">FIG. 7A</figref> to the last patterned mask layer <b>360</b>E of <figref idref="DRAWINGS">FIG. 7E</figref>. In this method, the duration of each of the leaching processes is not necessarily different (they may be the same or they may be different), but previously leached portions of the polycrystalline compact <b>302</b> are not shielded from the leaching agent in subsequent leaching processes, so that the depth of the leached portions increases with each sequential leaching process in which it is exposed to a leaching agent. Thus, as shown in <figref idref="DRAWINGS">FIGS. 7A through 7E</figref>, the leach depth in the first volume <b>320</b> gets deeper and deeper with each sequential leaching process. After completing the leaching processes, the last patterned mask layer <b>360</b>E may be removed to form the PDC cutting element <b>300</b> and the polycrystalline compact <b>302</b> of <figref idref="DRAWINGS">FIG. 7F</figref>, which is substantially identical to the PDC cutting element <b>200</b> of <figref idref="DRAWINGS">FIG. 6F</figref>, and includes an interface <b>330</b> between the first volume <b>320</b> and the second volume <b>322</b> having a stepped profile in a plane containing the central axis A, such as the plane of the cross-sectional view of <figref idref="DRAWINGS">FIG. 7F</figref>.

In additional embodiments of the present disclosure, the front cutting face of a polycrystalline compact may not be planar, and the front cutting face or a central portion thereof may have a generally concave shape. In such embodiments, a single leaching process may be used to form a first leached volume and a second unleached volume within the polycrystalline compact, and the interface between the first and second volumes may have a concave shape similar to that of the interfaces previously described herein. For example, <figref idref="DRAWINGS">FIG. 8</figref> illustrates a PDC cutting element <b>400</b> similar to those previously described herein. The PDC cutting element <b>400</b> includes a polycrystalline compact <b>402</b> on a substrate <b>404</b>. The polycrystalline compact <b>402</b> may be as previously described, except that a central portion of a front cutting face <b>408</b> of the polycrystalline compact <b>402</b> has a concave or dish shape as shown in <figref idref="DRAWINGS">FIG. 8</figref>. The polycrystalline compact <b>402</b> may be leached as previously described herein, with or without the use of any mask layer or mask device, such that the entire front cutting face <b>408</b> of the polycrystalline compact <b>402</b> is subjected to the leaching agent for at least substantially the same duration of time. As a result, an interface <b>430</b> between a leached first volume <b>420</b> and an unleached second volume <b>422</b> within the polycrystalline compact <b>402</b> may have a similar concave or dished shape, similar to the shape of the interfaces <b>130</b>, <b>230</b>, and <b>330</b> previously described herein.

<figref idref="DRAWINGS">FIG. 9</figref> is a simplified cross-sectional side view similar to those of <figref idref="DRAWINGS">FIGS. 6A-6F and 7A-7F</figref>, and illustrates another embodiment of a PDC cutting element <b>450</b> that includes a generally planar polycrystalline compact <b>452</b> on an end of a substrate <b>454</b>. The PDC cutting element <b>450</b> is shown in <figref idref="DRAWINGS">FIG. 9</figref> with a mask layer <b>460</b> over and encapsulating the polycrystalline compact <b>452</b> in preparation for a leaching process. In contrast to previous methods, however, the mask layer <b>460</b> may be permeable to a leaching agent that will be used to leach interstitial material out from interstitial spaces between grains of hard material in a region of the polycrystalline compact <b>452</b>. Thus, for example, the mask layer <b>460</b> may comprise a porous polymer or ceramic material. In particular, the mask layer <b>460</b> may comprise a porous material having a three-dimensional open pore network therein, such that a leaching agent may flow through the open pore network from the exterior surfaces of the mask layer <b>460</b> to the polycrystalline compact <b>452</b>. In such a configuration, the time required for the leaching agent to flow from an exterior surface of the mask layer <b>460</b> to the surface of the polycrystalline compact <b>452</b> may be at least partially a function of the distance through the mask layer <b>460</b> from the exterior surface of the mask layer <b>460</b> to the surface of the polycrystalline compact <b>452</b>, and, hence, the thickness of the mask layer <b>460</b>. The mask layer <b>460</b> thus may be formed to have a thickness that varies over a front cutting face <b>458</b> of the polycrystalline compact <b>452</b>, as shown in <figref idref="DRAWINGS">FIG. 9</figref>. By way of example and not limitation, a front surface <b>462</b> of the mask layer <b>460</b> may be machined or otherwise formed, prior to the leaching process, to have a concave or dish-shaped geometry, as shown in <figref idref="DRAWINGS">FIG. 9</figref>. In some embodiments, the front surface <b>462</b> of the mask layer <b>460</b> may be formed to have a geometry that generally corresponds to a desired geometry of an interface between a leached region and an unleached region to be defined within the polycrystalline compact <b>452</b> by a subsequent leaching process. Thus, the front surface <b>462</b> of the mask layer <b>460</b> may have a shape as described previously in relation to the interface <b>130</b> with reference to <figref idref="DRAWINGS">FIGS. 1, 2, and 5</figref> (or the shape of any other interface as described herein).

Due to the varying thickness of the mask layer <b>460</b> over the polycrystalline compact <b>452</b>, the effective residence time during which any particular region of the polycrystalline compact <b>452</b> will be subjected to the leaching agent will be at least partially a function of the thickness of the mask layer <b>460</b> overlying that particular region of the polycrystalline compact <b>452</b>. Regions of the polycrystalline compact <b>452</b> underlying thinner regions of the mask layer <b>460</b> will be subjected to the leaching agent for relatively longer residence times resulting in relatively deeper leaching depths therein, while regions of the polycrystalline compact <b>452</b> underlying thicker regions of the mask layer <b>460</b> will be subjected to the leaching agent for relatively shorter residence times resulting in shallower leaching depths therein. Thus, subjecting the PDC cutting element <b>450</b> of <figref idref="DRAWINGS">FIG. 9</figref> with the mask layer <b>460</b> thereon to a leaching process as previously described herein may result in the formation of a leached and unleached region within the polycrystalline compact <b>452</b> with an interface therebetween having a geometry as previously described herein.

Embodiments of cutting elements according to the present description, such as the PDC cutting elements <b>100</b>, <b>200</b>, <b>300</b>, <b>400</b>, may be secured to an earth-boring tool and used to remove subterranean formation material in a drilling operation or other operation used to form a wellbore in a subterranean formation. The earth-boring tool may comprise, for example, an earth-boring rotary drill bit, a percussion bit, a coring bit, an eccentric bit, a reamer tool, a milling tool, etc. As a non-limiting example, <figref idref="DRAWINGS">FIG. 10</figref> illustrates a fixed-cutter type earth-boring rotary drill bit <b>500</b> that includes a plurality of PDC cutting elements <b>100</b> (<figref idref="DRAWINGS">FIGS. 1 through 5</figref>), each of which includes a polycrystalline compact <b>102</b> as previously described herein. The rotary drill bit <b>500</b> includes a bit body <b>502</b>, and the PDC cutting elements <b>100</b> are bonded to the bit body <b>502</b>. The cutting elements <b>100</b> may be brazed, welded, or otherwise secured, within pockets <b>503</b> formed in the outer surface of the bit body <b>502</b>, as is known in the art. For example, the bit body <b>502</b> may include a plurality of blades <b>504</b> defining fluid courses and junk slots therebetween.

Additional non-limiting example embodiments of the disclosure are described below.

Embodiment 1

A generally planar polycrystalline compact, comprising: a body of inter-bonded grains of hard material having a first major surface defining a front cutting face of the polycrystalline compact, a second major surface on an opposing back side of the body, at least one lateral side surface extending between the first major surface and the second major surface, and a central axis extending through a center of the body and generally perpendicular to the first major surface and the second major surface, the hard material comprising diamond or cubic boron nitride; and an interstitial material; and wherein a first volume of the polycrystalline compact is at least substantially free of the interstitial material such that voids exist in interstitial spaces between surfaces of the inter-bonded grains of hard material within the first volume, a second volume of the polycrystalline compact includes the interstitial material in interstitial spaces between surfaces of the inter-bonded grains of hard material within the second volume, and an interface between the first volume and the second volume is configured, located and oriented such that at least one crack originating proximate a point of contact between the polycrystalline compact and a subterranean formation near the at least one lateral side surface of the body and propagating along the interface generally toward the central axis will propagate generally toward the second major surface of the body at an acute angle or angles to each of the first major surface and the second major surface.

Embodiment 2

The polycrystalline compact of Embodiment 1, wherein an annular portion of the interface between the first volume and the second volume is located a first distance from the second major surface of the body of inter-bonded grains of hard material, and regions of the interface circumscribed by the annular portion are located at one or more distances from the second major surface of the body of inter-bonded grains of hard material, each of the one or more distances being shorter than the first distance.

Embodiment 3

The polycrystalline compact of Embodiment 1 or Embodiment 2, wherein a first portion of the interface between the first volume and the second volume is located at a first distance from the second major surface of the body of inter-bonded grains of hard material and at a second distance from the central axis of the body of inter-bonded grains of hard material, and a second portion of the interface between the first volume and the second volume is located at a third distance from the second major surface of the body of inter-bonded grains of hard material and at a fourth distance from the central axis of the body of inter-bonded grains of hard material, the first distance being greater than the third distance, and the second distance being greater than the fourth distance.

Embodiment 4

The polycrystalline compact of any one of Embodiments 1 through 3, wherein at least a portion of the interface between the first volume and the second volume has substantially a dish shape.

Embodiment 5

The polycrystalline compact of any one of Embodiments 1 through 3, wherein at least a portion of the interface between the first volume and the second volume has a stepped profile in a plane containing the central axis.

Embodiment 6

The polycrystalline compact of any one of Embodiments 1 through 4, wherein at least a portion of the interface between the first volume and the second volume has a smooth profile in a plane containing the central axis.

Embodiment 7

The polycrystalline compact of any one of Embodiments 1 through 6, wherein the first major surface of the body of inter-bonded grains of hard material comprises a surface of the first volume of the polycrystalline compact.

Embodiment 8

The polycrystalline compact of any one of Embodiments 1 through 7, wherein the second major surface of the body of inter-bonded grains of hard material comprises a surface of the second volume of the polycrystalline compact.

Embodiment 9

The polycrystalline compact of any one of Embodiments 1 through 8, wherein at least a portion of the at least one lateral side surface of the body of inter-bonded grains of hard material comprises another surface of the first volume of the polycrystalline compact.

Embodiment 10

The polycrystalline compact of any one of Embodiments 1 through 9, wherein the first volume extends along the first major surface and along at least a portion of the at least one lateral side surface of the body of inter-bonded grains of hard material, and the second volume extends along the second major surface of the body of inter-bonded grains of hard material.

Embodiment 11

An earth-boring tool, comprising: a tool body; and a plurality of cutting elements attached to the tool body, wherein at least one cutting element of the plurality of cutting elements comprises a polycrystalline compact as recited in any one of Embodiments 1 through 10.

Embodiment 12

The earth-boring tool of Embodiment 11, wherein the earth-boring tool comprises at least one of a rotary drill bit for drilling a wellbore and a reamer for enlarging a wellbore.

Embodiment 13

A method of forming a generally planar polycrystalline compact, comprising: using a high-temperature/high-pressure (HTHP) sintering process to form a body of inter-bonded grains of hard material having a first major surface defining a front cutting face of the polycrystalline compact, a second major surface on an opposing back side of the body, at least one lateral side surface extending between the first major surface and the second major surface, and a central axis extending through a center of the body and generally perpendicular to the first major surface and the second major surface, the hard material comprising diamond or cubic boron nitride, using the high-temperature/high-pressure (HTHP) sintering process including catalyzing the formation of inter-granular bonds between the inter-bonded grains of hard material using a catalyst, the catalyst forming an interstitial material in the body of inter-bonded grains of hard material; and removing the interstitial material from interstitial spaces between surfaces of the inter-bonded grains of hard material within the first volume and leaving the interstitial material in interstitial spaces between surfaces of the inter-bonded grains of hard material within the second volume such that the first volume is at least substantially free of the interstitial material and voids exist in the interstitial spaces between surfaces of the inter-bonded grains of hard material within the first volume, and forming an interface between the first volume and the second volume configured, located and oriented such that at least one crack originating proximate a point of contact between the polycrystalline compact and a subterranean formation near the at least one lateral side surface of the body and propagating along the interface generally toward the central axis will propagate generally toward the second major surface at an acute angle or angles to each of the first major surface and the second major surface.

Embodiment 14

The method of Embodiment 13, wherein removing the interstitial material from interstitial spaces between surfaces of the inter-bonded grains of hard material within the first volume and leaving the interstitial material in interstitial spaces between surfaces of the inter-bonded grains of hard material within the second volume comprises: covering a portion of the first major surface of the body of inter-bonded grains of hard material with a first patterned mask layer; leaching a first portion of the body of inter-bonded grains of hard material through at least one aperture in the first patterned mask layer and removing the interstitial material from interstitial spaces between surfaces of the inter-bonded grains of hard material within the first portion of the body; removing the first patterned mask layer from the body; covering a portion of the first major surface of the body of inter-bonded grains of hard material with a second patterned mask layer different from the first patterned mask layer; and leaching a second portion of the body of inter-bonded grains of hard material through at least one aperture in the second patterned mask layer and removing the interstitial material from interstitial spaces between surfaces of the inter-bonded grains of hard material within the second portion of the body.

Embodiment 15

The method of Embodiment 13 or Embodiment 14, further comprising forming the interface such that an annular portion of the interface between the first volume and the second volume is located a first distance from the second major surface of the body of inter-bonded grains of hard material, and regions of the interface circumscribed by the annular portion are located at one or more distances from the second major surface of the body of inter-bonded grains of hard material, each of the one or more distances being shorter than the first distance.

Embodiment 16

The method of any one of Embodiments 13 through 15, further comprising forming the interface such that a first portion of the interface between the first volume and the second volume is located at a first distance from the second major surface of the body of inter-bonded grains of hard material and at a second distance from the central axis of the body of inter-bonded grains of hard material, and such that a second portion of the interface between the first volume and the second volume is located at a third distance from the second major surface of the body of inter-bonded grains of hard material and at a fourth distance from the central axis of the body of inter-bonded grains of hard material, the first distance being greater than the third distance, and the second distance being greater than the fourth distance.

Embodiment 17

The method of any one of Embodiments 13 through 16, further comprising forming at least a portion of the interface between the first volume and the second volume to have substantially a dish shape.

Embodiment 18

The method of any one of Embodiments 13 through 16, further comprising forming at least a portion of the interface between the first volume and the second volume to have a stepped profile in a plane containing the central axis.

Embodiment 19

The method of any one of Embodiments 13 through 16, further comprising forming at least a portion of the interface between the first volume and the second volume to have a smooth profile in a plane containing the central axis.

Embodiment 20

The method of any one of Embodiments 13 through 19, further comprising forming the first volume to extend along the first major surface and along at least a portion of the at least one lateral side surface of the body of inter-bonded grains of hard material, and forming the second volume to extend along the second major surface of the body of inter-bonded grains of hard material.

The foregoing description is directed to particular embodiments for the purpose of illustration and explanation. It will be apparent to one skilled in the art that many modifications and changes to the embodiments as set forth above are possible without departing from the scope of the embodiments disclosed herein as hereinafter claimed, including legal equivalents. For example, elements and features of one disclosed embodiment may be combined with the elements and features of other disclosed embodiments to provide further embodiments of the disclosure. It is intended that the following claims be interpreted to embrace all such modifications and changes.